Rotary apparatus for a gas turbine engine

ABSTRACT

Rotary apparatus ( 17 ) for a gas turbine engine ( 10 ) comprises a rotor assembly ( 63 ) and first and second stator assemblies ( 55, 59 ) mounted coaxially with respect to each other. The first stator assembly ( 55 ) is upstream of the second stator assembly ( 59 ), and the second stator assembly ( 59 ) is upstream of the rotor assembly ( 63 ). The rotor assembly ( 63 ) comprises an annular array ( 64 ) of rotor blades ( 66 ), and each stator assembly ( 55, 59 ) comprises an annular array ( 56, 60 ) of stator vanes ( 58, 62 ). Each vane ( 58, 62 ) has a leading edge and a trailing edge. The stator assemblies ( 55, 59 ) are circumferentially translatable relative to each other between a first condition in which each of the vanes ( 62 ) of the second stator assembly ( 59 ) is substantially aerodynamically aligned with a respective one of the vanes ( 58 ) of the first stator assembly ( 55 ), and a second condition in which the vanes ( 58,62 ) of the first and second stator assemblies ( 55, 59 ) are out of aerodynamic alignment with each other. In the first condition, at least a part of each vane ( 62 ) of the second stator assembly ( 59 ) extends beyond the trailing edge of the respective vane ( 58 ) of the first stator assembly ( 55 ).

[0001] This invention relates to rotary apparatus for gas turbineengines. In particular, but not exclusively, the invention relates tointermediate pressure turbines.

[0002] In a three shaft gas turbine engine, in which the intermediatepressure compressor is driven by the intermediate pressure turbine, thedesign of the intermediate pressure compressor is dominated by itsperformance at low power. Attempts have been made to enable the capacityof the intermediate pressure turbine to vary with the power of theengine, but these generally require large numbers of working parts,making the turbines prone to maintenance problems and expensive.

[0003] According to one aspect of this invention there is provided arotary apparatus for a gas turbine engine, the apparatus comprisingfirst and second stator assemblies and a rotor assembly mountedcoaxially with respect to each other, the first stator assembly beingupstream of the second stator assembly, and the second stator assemblybeing upstream of the rotor assembly, the rotor assembly comprising anannular array of rotor blades, and each stator assembly comprising anannular array of stator vanes, each vane having a leading edge and atrailing edge wherein the vanes of one of the stator assemblies aremovable relative to the vanes of the other of the stator assembliesbetween a first condition in which each of the vanes of the secondstator assembly is substantially in aerodynamic alignment with arespective one of the vanes of the first stator assembly, and the exitangle of gas from the stator assemblies is relatively high, and a secondcondition in which the exit angle of gas from the stator assemblies isrelatively low. Thus, in the first condition, at least a part of eachvane of the second stator assembly extends beyond the trailing edge ofthe respective vane of the first stator assembly.

[0004] The rotary apparatus may be a turbine, preferably an intermediatepressure turbine. Alternatively, the rotary apparatus may be acompressor.

[0005] When the stator assemblies are in the second condition, the vanesof the first and second stator assemblies may be out of aerodynamicalignment with each other.

[0006] The first and second stator assemblies are preferablycircumferentially translatable relative to each other. The first statorassembly may be fixed and the second stator assembly may be translatablerelative to the first stator assembly. Preferably the vanes of thesecond stator assembly extend downstream beyond the trailing edges ofthe vanes of the first stator assembly.

[0007] The vanes of the first and second stator assemblies arepreferably configured such that, in the first condition, the exit angleof the gas from the stator assemblies is controlled by the vanes of thefirst and the second stator assemblies, whereby said gas is directed, inuse, from the stator arrangement at a relatively high exit angle. Theconfiguration of the varies of the first and second stator assemblies ispreferably such that in the second condition, the exit angle of said gasis controlled to a major degree, and preferably substantially wholly, bythe vanes of the first stator assembly only, whereby said gas isdirected, in use, from the stator arrangement at a relatively low exitangle. The first and second stator assemblies are preferably relativelytranslatable to any condition intermediate the first and secondconditions.

[0008] In the first condition, the vanes of the second stator assemblyare preferably arranged such that the leading edge of each vane of thesecond stator assembly is provided in aerodynamic close proximity to, orin abutment with, the trailing edge of the respective vanes of the firststator assembly.

[0009] In the second condition, the leading edge of each vane of thesecond stator assembly is preferably spaced aerodynamically from thetrailing edge of the closest vane of the second stator assembly.

[0010] Preferably, when the stator assemblies are in the secondcondition, the vanes of the second stator assembly are arrangedintermediate the vanes of the first stator assembly. In one embodiment,the vanes of the second stator assembly are arranged generally parallel,in use, to the flow of gas around the vanes of the first statorassembly. In another embodiment, the vanes of the second stator assemblyare arranged substantially mid-way between the adjacent vanes of thefirst stator assembly.

[0011] In one embodiment, the vanes of the second stator assembly arearranged wholly downstream of the vanes of the first stator assembly. Inthis embodiment, the vanes of the second stator assembly may betranslated between the first and second conditions across the trailingedge of the respective vanes of the first stator assembly.

[0012] In another embodiment, the leading edge of each vane of thesecond stator assembly may overlap the trailing edge of a respective oneof the vanes of the first stator assembly. In this embodiment, the vanesof the second stator assembly may be translated between the first andsecond conditions across the respective flow paths defined betweenadjacent vanes of the first stator assembly.

[0013] The first stator assembly may include fixed support means tosupport the vanes thereof. The second stator assembly may includetranslatable support means to support the vanes thereof. Thetranslatable support means may comprise an annular member and may bemovably mounted on the fixed support means.

[0014] The fixed support means may comprise an inner member, which maybe annular, extending radially inwardly of the vanes, and may alsoinclude an outer member, which may be annular, extending radiallyoutwardly from the vanes. Seal means may be provided between the firstand second stator assemblies. Preferably the seal means comprises a sealextending between the fixed support means and the translatable supportmeans. In the preferred embodiment, the seal means comprises a firstseal extending between the inner member of the fixed support means andthe translatable support means, and between the outer member and thesecond stator assembly.

[0015] The apparatus may include actuating means to effect translationof the second stator assembly.

[0016] In one embodiment, a bearing may be provided between the fixedsupport means and the translatable support means. Preferably, thebearing is provided between the inner member and the translatablesupport means. The inner member may be provided with a flange extendingtowards the translatable support means, and the bearing may be providedbetween the translatable support means and said flange.

[0017] Alternatively, connecting members may be provided between thefixed support means and the translatable support means. In oneembodiment, the connecting members comprise a plurality of plates whichmay be arranged circumferentially, preferably substantially uniformlyspread, around the stator arrangement extending between the inner memberand the translatable support member. Each plate is preferably angledsuch that it extends substantially parallel to the direction of aerofoillift on the vanes of the second stator assembly. The plates areadvantageously flexible in the circumferential direction to allowmovement of the second stator assembly between said first and secondconditions.

[0018] In another embodiment, the connecting members comprise aplurality of rods pivotally mounted at each end thereof to therespective first and second stator assemblies. Preferably, the rods aremounted to the inner member and to the translatable support means. Inthis embodiment, the rods are preferably angled to be substantiallyparallel to the direction of aerofoil lift on the vanes of the secondstator assembly.

[0019] In an another embodiment, the connecting members comprise aplurality of circumferentially extending struts arranged in compressionbetween the first and second stator assemblies. Preferably between theinner member and the translatable support means. The struts arepreferably angled relative to the first and second stator assemblies,such that they are substantially parallel to the direction of aerofoillift on the vanes of the second stator assembly. In this embodiment, thetranslatable support means may comprise a flange extending upstream ofthe second stator assembly, and having thereon a radially outwardlyextending lip. The fixable means may include a radially inwardlysupporting lip and the struts may extend between said lips.

[0020] An embodiment of the invention will now be described by way ofexample only with reference to the accompanying drawings, in which:

[0021]FIG. 1 is a sectional side view of the upper half of a gas turbineengine;

[0022]FIG. 2 is a part cut away section of the turbine arrangements ofan example of the engine shown in FIG. 1;

[0023]FIG. 3 is a schematic sectional circumferential view of rotaryapparatus;

[0024]FIG. 4 is a diagrammatic radial view of a stator arrangement in afirst condition;

[0025]FIG. 5 is a diagrammatic radial view of a stator arrangement in asecond condition;

[0026]FIG. 6 is a diagrammatic radial view of a further embodiment of astator arrangement showing the first and second condition;

[0027]FIG. 7 is a schematic circumferential view of a further embodimentof a stator arrangement;

[0028]FIG. 8 is one example of the view along the lines A-A in FIG. 7;

[0029]FIG. 9 is a view of an alternative arrangement along the lines A-Ain FIG. 7;

[0030]FIG. 10 is a further example of a support for the stator vanearrangement;

[0031]FIG. 11 is one example of the view along the lines B-B in FIG. 10.

[0032] Referring to FIG. 1, a gas turbine engine is generally indicatedat 10 and comprises, in axial flow series, an air intake 11, apropulsive fan 12, an intermediate pressure compressor 13, a highpressure compressor 14, combustion equipment 15, a turbine arrangementcomprising a high pressure turbine 16, an intermediate pressure turbine17, a low pressure turbine 18 and an exhaust nozzle 19.

[0033] The gas turbine engine 10 works in a conventional manner so thatair entering the intake 11 is accelerated by the fan 12 which producetwo air flows: a first air flow into the intermediate pressurecompressor 13 and a second air flow which provides propulsive thrust.The intermediate pressure compressor compresses the air flow directedinto it before delivering that air to the high pressure compressor 14where further compression takes place.

[0034] The compressed air exhausted from the high pressure compressor 14is directed into the combustion equipment 15 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive, the high, intermediate and lowpressure turbines 16, 17 and 18 before being exhausted through thenozzle 19 to provide additional propulsive thrust. The high,intermediate and low pressure turbine 16, 17 and 18 respectively drivethe high and intermediate pressure compressors 14 and 13, and the fan 12by suitable interconnecting shafts.

[0035] Referring to FIG. 2, there is shown an example of a turbinearrangement which comprises a casing 24 surrounding the high,intermediate and low pressure turbines 16, 17 and 18. The turbinearrangement and, consequently, the low intermediate and high pressureturbines having a principal axis Y-Y.

[0036] The high and intermediate pressure turbines 16 and 17 are singlestage turbines, whereas the low pressure turbine is a multiple stageturbine comprising two stages. The high pressure turbine 16 drives thehigh pressure turbine shaft 26. The intermediate pressure turbine 17drives the intermediate pressure turbine shaft 28, and the low pressureturbine 18 drives the low pressure turbine shaft 30.

[0037] The high pressure turbine 16 comprises a high pressure statorassembly 31 in the form of an annular array 32 of fixed nozzle guidevanes 34 arranged upstream of a high pressure rotor assembly 35comprising an annular array 36 of turbine blades 38.

[0038] The low pressure turbine 18 comprises a first low pressure statorassembly 39 comprising a first array 40 of nozzle guide vanes 42arranged upstream of a first upstream low pressure rotor assembly 43comprising a first array 44 of turbine blades 46. This constitutes thefirst stage of the low pressure turbine 18. Arranged downstream of thearray 44 of rotor blades 46 is a second low pressure stator assembly 47comprising a second array 48 of fixed nozzle guide vanes 50. Arrangedimmediately downstream of the fixed nozzle guide vanes 50 is a secondlow pressure rotor assembly 51 comprising an array 52 of turbine blades54. The nozzle guide vanes 50 and the turbine blades 54 constitute thesecond stage of the two stage low pressure turbine 18.

[0039] The single stage intermediate pressure turbine 17 comprises afirst intermediate pressure stator assembly 55 and a second intermediatepressure stator assembly 59. The first intermediate pressure statorassembly 55 comprises an annular array 56 of fixed nozzle guide vanes58. Arranged immediately downstream of the fixed nozzle guide vanes 58is a second intermediate pressure stator assembly 59 comprising anannular array 60 of circumferentially translatable nozzle guide vanes62. An intermediate pressure rotor assembly 63 is provided immediatelydownstream of the translatable nozzle guide vanes 62, and comprises anannular array 64 of rotor blades 66.

[0040]FIG. 3 is a schematic diagram viewed in the circumferentialdirection of the intermediate pressure turbine 17 shown in FIG. 2.

[0041] The first intermediate pressure stator assembly 55 comprises asupport arrangement 68 for the fixed nozzle guide vanes 58. The supportarrangement 68 comprises a radial support member 70 extending radiallyinwardly from an inner annular support shroud 72. A first flange 74extends from the radial support member 70 to provide support for thesecond intermediate pressure stator assembly 59. The nozzle guide vanes62 are supported by an annular rim 76. An inner annular shroud 78 isprovided on the rim 76 and the translatable nozzle guide vanes 62 aremounted on the shroud 78. A bearing 80 is provided between the rim 76and the flange 74 to allow circumferential translation of the rim 76and, correspondingly, of the nozzle guide vanes 62 relative to theflange 74.

[0042] A further flange member 80 extends from the support member 44towards the annular rim 76, and a flange member 82 extends from theannular rim 76 towards the support member 70. The flange members 80, 82overlap each other and a labyrinth seal 84 is provided therebetween toprevent the leakage of hot air from the turbine 17.

[0043] An outer annular shroud 86 is provided on the opposite edge ofthe fixed nozzle guide vanes 58 to the inner shroud 72. The outer shroud86 has extending therefrom a flange member 88 which extends across thetranslatable nozzle guide vane 62. An outer annular shroud 90 isprovided on the opposite edges of the translatable nozzle guide vanes 62to the inner shroud 78, and. a labyrinth seal 92 extends between theflange member 88 and the outer shroud 90 to prevent leakage of hotgases.

[0044] Actuator means 94, which could be any suitable actuator meansknown in the art, is provided to effect the circumferential translationof the second intermediate pressure stator assembly 59.

[0045] Referring to FIGS. 4 and 5, there is shown schematically thefirst and second intermediate pressure stator assemblies 55 and 59. Thefixed nozzle guide vanes 58 are circumferentially uniformly spaced andsupported on the inner shroud 72. However for clarity only two of thefixed nozzle guide vanes 58 are shown. The translatable nozzle guidevanes 62 are similarly circumferentially uniformly spaced from eachother, and supported on the inner shroud 78. the pitch between thetranslatable nozzle guide vanes 62 is approximately equal to the pitchbetween the fixed nozzle guide vanes 58.

[0046] In FIG. 4, the translatable nozzle guide vanes 62 are in a firstcondition, in which the translatable nozzle guide vanes 62 are arrangedin aerodynamic alignment with the fixed nozzle guide vanes 58. As can beseen the translatable nozzle guide vanes 62 extend wholly beyond anddownstream of the trailing edges of the fixed nozzle guide vanes 58. Inthis first condition, air is directed between the nozzle guide vanes 58,62 by the combination of the configurations of the fixed nozzle guidevanes 58 and the translatable nozzle guide vanes 62 such that the airexits at a high exit angle from the second intermediate pressure statorassembly 59. This represents the normal running condition of the engineand, in this condition, the intermediate pressure turbine is running atlow capacity.

[0047] Referring to FIG. 5, there is shown the same apparatus as in FIG.4, but in which the translatable nozzle guide vanes 62 have beentranslated to the second condition, in which the translatable nozzleguide vanes 62 are disposed in a position intermediate adjacent fixednozzle guide vanes 58. In this second condition, the air passing throughthe first and second intermediate pressure stator vane assemblies 55 and59 directed mainly by the fixed nozzle guide vanes 58. The translatablenozzle guide vanes 62 have little or no effect on the exit angle of theair, and the configuration of 35 the fixed nozzle guide vanes 58 is suchthat the vanes 58 direct the air at a relatively low exit angle from thesecond intermediate pressure stator vane assembly 59. This representsthe engine running at low power and the intermediate pressure turbinerunning at a high capacity.

[0048] Referring to FIG. 6, there is shown a modification to theembodiment shown in FIGS. 4 and 5. In FIG. 6, only one fixed nozzleguide vane 58 is shown, having leading and trailing edges 58A and 58Brespectively. Also shown are lines 96 representing the direction of flowof air around the nozzle guide vanes 58. The solid lines 96 representthe direction that air would flow if no translatable nozzle guide vanes62 were present. FIG. 6 also shows two translatable nozzle guide vanes62. One of the translatable nozzle guide vanes is shown in solid linesand designated 62A. The nozzle guide vane 62A is shown in the firstcondition. A further nozzle guide vane is shown in dotted lines anddesignated 62B in FIG. 6. The translatable nozzle guide vane 62B is inthe second condition.

[0049] In the first condition, the translatable nozzle guide vanes 62,as represented by the nozzle guide vane 62A, are arranged in aerodynamicalignment with the fixed nozzle guide vanes 58, and the combinationdirects air in the direction shown by the dotted lines 96A. Thus, as canbe seen, the air exits from the second intermediate pressure statorassembly 59 at a high exit angle.

[0050] When the translatable nozzle guide vane 62 are moved to thesecond condition, as represented by the nozzle guide vane 62B, thetranslatable nozzle guide vanes 62B are generally parallel with thedirection of flow of air over the fixed nozzle guide vane 58. Thus, inthis condition, the air flow substantially follows the solid lines 96and exits from the annular array 60 at a low exit angle.

[0051] As can be seen the leading edge 63A of the translatable nozzleguide vane 62A overlaps the trailing edge of the fixed nozzle guide vane58, whereas the trailing edge 63B extends beyond and downstream of thetrailing edge 58B of the fixed nozzle guide vane 58. Consequently, thisembodiment cannot be moved between the first and second conditions bytranslation across the trailing edge of the fixed nozzle guide vane 58.Instead, the translatable nozzle guide vanes 62 must be moved from thefirst condition to the second condition and vice-versa across the flowpath between adjacent fixed nozzle guide vanes 58.

[0052] The provision of two sets of nozzle guide vanes 58, 62 to directair onto the turbine blades of the intermediate pressure turbine 17 canvary the capacity of the turbine by varying the exit angle of the airfrom the second intermediate pressure stator assembly 59. The ability tovary the capacity of the intermediate pressure turbine 17 between normalrunning conditions and lower power of the engine has implications forthe design of the intermediate pressure compressor. By varying thecapacity of the intermediate pressure turbine, the number of compressorblades can be halved, and it is possible to avoid the use ofintermediate pressure compressor variables and bleeds. It would alsomean that the high pressure compressor operating point is made almostconstant to allow its pressure ratio to be increased without the use ofvariables.

[0053] FIGS. 7 to 11 show various alternative constructions for thesupport and actuation of the stator vane arrangement 20.

[0054] Referring to FIG. 7, there is shown a modification to the designshown in FIG. 3, in which the same features have been given the samereference numeral. In the embodiment shown in FIG. 7, the translatablenozzle guide vanes 62 are held between concentrically mounted inner andouter annular shrouds 78, 90 each of which has a respective flange 98,100 extending over the fixed nozzle guide vanes 58. The fixed nozzleguide vanes 58 are held between concentrically mounted inner and outerannular shrouds 72, 86. A labyrinth seal 102 is provided between theflange 98 and the annular shroud 72 and a labyrinth seal 104 is providedbetween the flange 100 and the outer annular shroud 86.

[0055] A plurality of elongate connecting members 106 extend between theinner annular shroud 78 and the support member 79. The connectingmembers 106 may be arranged at an angle of between 30 and 45° to theprincipal axis Y-Y of the intermediate pressure turbine 17. This anglecorresponds to the direction of aerofoil lift on the translatable nozzleguide vanes 62.

[0056] The connecting members 80 are provided radially inwardly of thefixed and translatable nozzle guide vanes 58, 62 and arecircumferentially uniformly spaced. A similar array of circumferentiallyuniformly spaced connecting members 108 is provided radially outwardlyof the nozzle guide vanes 58, 62. The connecting members 108 extendbetween the outer annular shroud 90 and a radially outwardly projectingflange 110 extending from the outer annular shroud 86 of the fixednozzle guide vanes 58.

[0057] The fact that the connecting members 80, 82 are arranged parallelto the direction of lift of the translatable nozzle guide vanes 28,means that the load required to circumferentially translate thetranslatable nozzle guide vanes 62 is minimised.

[0058]FIGS. 8 and 9 are views along the lines A-A in FIG. 7 and showalternative embodiments for the connecting members 106, 108. In FIG. 8,the connecting members 106 are in the form of substantially flat platesfixedly mounted between the support member 70 and the inner annularshroud 78. Similar substantially flat plates (not shown) are connectedbetween the outwardly projecting flange 110 and the outer annular shroud90. The plates are resiliently deformable in the circumferentialdirection of the turbine 17. When the actuator (not shown in FIGS. 7 or8) applies a force in the direction indicated by the arrow A totranslate the nozzle guide vanes 62 in the same direction, the platesresiliently bend accordingly. When a force is applied by the actuator(not shown) in the opposite direction, indicated by the arrow B, theplates resiliently bend in that direction.

[0059] Referring to FIG. 9, the connecting members 106 are in the formof elongate rods pivotally mounted by pivots 112 at their opposite endregions 114 respectively to the support member 70, and to the innerannular shroud 78. When the actuator applies a force to translate thetranslatable nozzle guide vanes 62 in the direction of arrow A, the rodspivot in the same direction, at their ends 114 to allow the nozzle guidevanes 62 to be translated in that direction. Similarly, when a force isapplied by the actuator means in the opposite direction indicated by thearrow B, the rods will pivot about their end 114 in the oppositedirection.

[0060] Further modifications to the support arrangement for the nozzleguide vanes 58, 62 are shown in FIGS. 10 and 11, in which the innerannular shroud 78 is provided with a flange 116 extending radiallyinwardly of the nozzle guide vanes 58 and a radially outwardly extendinglip 118 extends from the flange 116. Similarly, a radially inwardlyextending lip 120 extends from the inner annular shroud 72 of the fixednozzle guide vanes 58. The lip 120 extends radially inwardly adjacentthe inner annular shroud 78. Connecting means in the form of acompression strut 122 (see also FIG. 11) is provided between the lips118, 114. Each compression strut has widened end regions 124 which arereceived in correspondingly configured recesses 126 in the lips 118 and120. the compression struts 122 are each aligned parallel to thedirection of aerofoil lift on the translatable nozzle guide vanes 62,and allows the actuator means to move the second stator main assembly 26in the directions indicated by the arrows A and B.

[0061] Various modifications can be made without departing from thescope of the invention, for example other means for connecting theannular member supporting the fixed and translatable vanes 24, 26 may beused. In addition, the use of translatable stator vanes can be appliednot just to the intermediate pressure turbine but also to thecompressors and other turbines.

[0062] Whilst endeavouring in the foregoing specification to drawattention to those features of the invention believed to be ofparticular importance it should be understood that the Applicant claimsprotection in respect of any patentable feature or combination offeatures hereinbefore referred to and/or shown in the drawings whetheror not particular emphasis has been placed thereon.

We claim:
 1. A rotary apparatus for a gas turbine engine, the apparatuscomprising first and second stator assemblies and a rotor assemblymounted coaxially with respect to each other, the first stator assemblybeing upstream of the second stator assembly, and the second statorassembly being upstream of the rotor assembly, the rotor assemblycomprising an annular array of rotor blades, and each stator assemblycomprising an annular array of stator vanes, each vane having a leadingedge and a trailing edge wherein the vanes of one of the statorassemblies are movable relative to the vanes of the other of the statorassemblies between a first condition in which each of the vanes of thesecond stator assembly is substantially in aerodynamic alignment with arespective one of the vanes of the first stator assembly, and the exitangle of gas from the stator assemblies is relatively high, and a secondcondition in which the exit angle of gas from the stator assemblies isrelatively low.
 2. A rotary apparatus according to claim 1 wherein whenthe stator assemblies are in the second condition, the vanes of thefirst and second stator assemblies are out of aerodynamic alignment witheach other.
 3. A rotary apparatus according to claim 1 wherein the firstand second stator assemblies are circumferentially translatable relativeto each other.
 4. A rotary apparatus according to claim 3 wherein thefirst stator assembly is fixed and the second stator assembly istranslatable relative to the first stator assembly.
 5. A rotaryapparatus according to claim 1 wherein the vanes of the second statorassembly extend downstream beyond the trailing edges of the vanes of thefirst stator assembly.
 6. A rotary apparatus according to claim 1wherein, in the first condition, the vanes of the second stator assemblyare arranged such that the leading edge of each vane of the secondstator assembly is provided in aerodynamic close proximity to, or inabutment with, the trailing edge of the respective vane of the firststator assembly.
 7. A rotary apparatus according to claim 1 whereinvanes of the first and second stator assemblies are configured suchthat, in the first condition, the exit angle of the gas from the statorassemblies is controlled by the vanes of the first stator assembly andby the vanes of the second stator assembly, whereby said gas isdirected, in use, from the stator arrangement at a relatively high exitangle, and in the second condition, the exit angle of said gas iscontrolled to a major degree by the vanes of the first stator assemblyonly, whereby said gas is directed, in use, from the stator assembliesat a relatively low exit angle.
 8. A rotary apparatus according to claim1 wherein the first and second stator assemblies are translatable to anycondition intermediate the first and second conditions.
 9. A rotaryapparatus according to claim 1 wherein, when the stator assemblies arein the second condition, the vanes of the second stator assembly arearranged intermediate the vanes of the first stator assembly.
 10. Arotary apparatus according to claim 9 wherein, when the statorassemblies in the second condition the vanes of the second statorassembly are arranged generally parallel, in use, to the flow of gasaround the vanes of the first stator assembly.
 11. A rotary apparatusaccording to claim 9 wherein, when the stator assemblies are in thesecond condition, the vanes of the second stator assembly are arrangedsubstantially midway between the adjacent vanes of the first statorassembly.
 12. A rotary apparatus according to claim 1 wherein the vanesof the second stator assembly are arranged wholly downstream of thevanes of the first stator assembly, and the vanes of the second statorassembly can be translated between the first and second conditionsacross the trailing edge of the respective vanes of the first statorassembly.
 13. A rotary apparatus according to claim 1 wherein theleading edge of each vane of the second stator assembly overlaps thetrailing edge of a respective one of the vanes of the first statorassembly, and the vanes of the second stator assembly can be translatedbetween the first and second conditions across the respective pathsdefined between adjacent vanes of the first stator assembly.
 14. Arotary apparatus according to claim 1 wherein the first stator assemblyincludes fixed support means to support the vanes thereof, and thesecond stator assembly includes translatable support means to supportthe vanes thereof.
 15. A rotary apparatus according to claim 14 whereinthe fixed and the translatable support means each comprises an innerannular member extending radially inwardly of the respective vanes, andan outer annular member extending radially outwardly of the respectivevanes.
 16. A rotary apparatus according to claim 15 wherein seal meansis provided between the first and second stator assemblies.
 17. A rotaryapparatus according to claim 16 wherein the seal means extends betweenthe fixed support means and the translatable support means.
 18. A rotaryapparatus according to claim 17 wherein the seal means comprises a firstseal extending between the inner member of the fixed support means andthe translatable support means, and between the outer member and thesecond stator assembly.
 19. A rotary apparatus according to claim 15wherein a bearing is provided between the fixed support means and thetranslatable support means.
 20. A rotary apparatus according to claim 19wherein the bearing is provided between the inner annular member and thetranslatable support means, the inner annular member being provided witha flange extending towards the translatable support means, and thebearing being provided between the translatable support means and saidflange.
 21. A rotary apparatus according to claim 15 wherein connectingmembers are provided between the fixed support means and thetranslatable support means.
 22. A rotary apparatus according to claim 21wherein the connecting members are circumferentially uniformly spacedaround the stator arrangement.
 23. A rotary apparatus according to claim16 wherein a plurality of connecting members are provided radiallyinwardly of the stator vanes and a plurality of further connectingmembers are provided radially outwardly of the stator vanes.
 24. Arotary apparatus according to claim 23 wherein the radially inwardconnecting members extend between said inner annular members of thefixed and translatable support means, and the radially outwardlyconnecting members extend between said outer annular members of thefixed and translatable support means.
 25. A rotary apparatus accordingto claim 21 wherein each connecting member is angled relative to theprincipal axis of the rotary apparatus such that each connecting memberextends substantially parallel to the direction of aerofoil lift on thevanes of the second stator assembly.
 26. A rotary apparatus according toclaim 21 wherein the connecting members comprise a plurality of plates,each plate being flexible in the circumferential direction to allow saidrelative translation of the first and second stator assemblies betweensaid first and second conditions.
 27. A rotary apparatus according toclaim 21 wherein the connecting members comprise a plurality of rodspivotally mounted at each end thereof to the respective first and secondstator assemblies.
 28. A rotary apparatus according to claim 21 whereinthe connecting members comprise a circumferentially extending strutsarranged in compression between the first and second stator assemblies.29. A rotary apparatus according to claim 28 wherein the translatablesupport means comprises a flange extending upstream of the second statorassembly, and having thereon a radially outwardly extending lip, thefixed support means including a radially inwardly supporting lip and thestruts extending between said lips.
 30. A rotary apparatus according toclaim 1 in the form of a turbine or a compressor.
 31. A rotary apparatusaccording to claim 1 in the form of an intermediate pressure turbine.32. A gas turbine engine including a rotary apparatus as claimed inclaim 1 .